Abrading apparatus



May 4, 1948. J. R. TURNER ABRADING APPARATUS Filed Feb. 24, 1947 FIG.1.,

FIG. 2.".

JOHN R TURNER vINI/'ENTOR BY mm i ORNEYS` Patented May 4, 1948 ABRADINGAPPARATUS John R. Turner, Rochester, N. Y., assignor to Eastman KodakCompany, Rochester, N. Y., a corporation of New Jersey ApplicationFebruary 24, 1947, Serial No. 730,387

7 Claims. l

The present invention relates to an abrading apparatus and particularlyto means for blocking work duringr the abrading thereof.

In the optical art, it is the usual practice to mount thin lenses ormirrors against a strong supporting tool by means of pitch or wax inorder to hold them during the abrading operation of one surface. This islikely to cause some springing or distortion of the lens 4or mirrorunless done very carefully. Even then, when large elements are beingworked upon, e. g., 9-inch mirrors, etc., it has been found almostimpossible to block the optical elements in this manner withoutincurring some undesirable distortion of the element. In addition, whenpitch and wax are used in blocking opticalelements, it is not unusual tohave to wait as much as two hours, or more, for the pitch or wax to'sufficiently cool and set before the abrading operation can be started.This time varies with the volume of the pitch or wax required for theblocking job and constitutes a considerable loss of time. Furthermore,in order that the supporting member will not be subject to flexure whichwould affect the uniformity of pressure applied to the work, it isimperative that this supporting member be absolutely rigid. For largepieces of work, the weight of the supporting member, in order to' besuiliciently rigid, is inconveniently great and causes the driving meansof the abrading apparatus to become overloaded.

The primary object of the present invention is to provide a blockingmeans for holding a piece of work during the abrading operation of onesurface thereof which overcomes all of the above'- mentioneddisadvantages of the conventional blocking systems. I

Specifically, the objects of the present invention are to provide ablocking means for an element being abraded by the use of which auniform pressure is applied to the element during the abradingoperation, so that the element is not distorted by non-uniformity of theapplied pres'- sure; to provide a blocking means which eliminates theuse of pitch and wax and consequently the time wasted inwaiting forthesev substances to set; to provide a blocking means which permits theuse of a light-supporting member, or chuck, for the work; and to providea blocking means which eliminates the need for skilled operators tocarry out the blocking operation.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionVitself, however, both as to its organization and its 2 methods ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description I when read inconnection with the accompanying drawings, in which:

Fig. 1 is a vertical section showing Ia chuck or blocking meansconstructed in accordance with a preferred embodiment of my inventionand particularly designed for holding a concave mirror during theabrading of the' concave surface thereof;

Fig. 2 is a plan view of a preferred form of hydrostatic cushion forminga part of the present invention; and

Fig. 3 is an enlarged sectional detail of a por- .tion of Fig. 1, andshowing how the mirror is supported by the hydrostatic cushion locatedbetween the same and the bottom of the recess in the chuck. Y

Like reference characters refer to corresponding parts throughout thedrawings.

Briefly, according to the present invention the element to be abraded isloosely confined in a recess in a chuck member atop a hydrostaticcushion seated between the same and the bottom of the recess. Theelement and/or cushion are held in the recess of the chuck by theabrading tool and by virtue of the hydrostatic nature of the cushion, auniform uid pressure is applied over the entire back ci the opticalelement Without permitting excessive displacement von one side whenonlya portion ofr the surface is in contact with the abrading tool, or forany other reason. The chuck need not be any thicker than is necessary tocarry the applied load since moderate ilexure of this member has noeiect on the uniformity of the pressure applied to the piece of work bythe cushion.

Coming now to the drawing wherein a preferred embodiment of theinvention for blocking a concave optical mirror is shown, the presentinvention consists of a light-weightv blocking chuck Ill having theusual socket member Il formed in the back surface thereof into which theball end I2 of an oscillating spindle I3 engages. This oscillatingspindle is reciprocated in the direction shown by the arrows by meansnot shown to oscillate the work relative to the rotat ing abrading toolas is well known in the art. The backing chuck l0 may be relativelylight compared to conventional equivalent structures and may includestrengthening ribs I4, as shown, .to reduce chances ofeXure.

The concave mirrorA I5 to be abraded is loosel ccnned in a recess i6 inthe face of the chuck and work is applied through spindle I3 by the useof weights, springs, or other conventional means.

In its preferred form, the hydrostatic cusl'ib'i consists of a spiral ofthin rubber tubing filled with a liquid, as shown in Fig. 2. Thiscushion substantially covers the entire bottom of the recess I6 in thechuck and forms a support for substantially every point on the backofthe mirror being abraded. The viscosity of the liquid is so chosen as toapply a uniform fluid pressure over the mirror Without excessivedisplacement on one side when only a portion of the surface of themirror is in contact with the polishing tool. For example, when thechuck 'moves to one of its extreme positions of oscillation,wherein thetool engages only a'fraction of the surface of the mirror, the increasedpressure on one side will cause: the fluid in the cushion to shift tothe side where the pressure is less until the pressure over the entiresurface of the work and chuck is equalized. If the rubber tubing isthin, and the liquid used is not too viscous, the hydrostatic responseof this cushion will be substantially immediate and continuous.

This arrangement of parts provides that the chuck need not be anythicker than is necessary to carry the applied load because moderateilexure of this member has no effect on the uniformity of the pressureapplied to the work by the cushion. While I have., shown the hydrostaticcushion as being of spiral form, it is pointed out that this is merely amatter of choice based on convenience of handling and fabrication. Thecushion -could just as well be of any other form, e. g., a single closedchamber, so long as every part of its interior is in iiuid communicationwith every other part of the interior. By the same token, while I havefound Water to vbe a suitable uid in synthetic rubber tubing in a chuckmember for blocking 9-inch mirrors at a tool speed of approximately 60R. P. M., it willzbe obvious that different fluids of varying viscosity,and -tubing of other elastic material than synthetic rubber, may befound more suitable for other projects and operating speeds.

The continuous length of the tube in the disclosed cushion distributesthe hydrostatic pressure uniformly. The vis-cosity of the fluid and theslight stiffness in the rubber-tubing prevents all of the fluid frombeing forced to one side of the cushion, .except when the system is notbeing rotated. It may prove advantageous to connect the inner and outerextremities of the spiral or to interconnect across sofme of the turns,if very small tubing is employed, in order to minimize Weight. In theevent that this form of chuck is used on a high-speed machine so thatthe centrifugal force set up in the fluid in the cushion would tend toupset the hydrostatic function thereof, then it is advisable to use airor some other suitable gas in the cushion. This substitution of fluidsis recommended for the obvious reason that a gas will not be affected by4 centrifugal forces set up by high-speed rotation of the chuck.

The present chuck is adaptable to easy blocking of the work, since allthat is required is to slip the element and cushion into the recess I6in proper superposed relation and to hold them in such position untilthe combination is slipped into operating relationship with the tool. Ifdesired, the hydrostatic cushion may be glued, or otherwise fastened, tothe bottom of the recess in the chuck so that it will not fall out withthe work when the chuck is removed from operative relationship withrespect to the tool. Referring to Fig. l, it will be noticed that theside walls of the recess in the chuck are adapted to engage and confinethe edges of the mirror to prevent the piece ofwork from slidinglaterally from beneath the chuck as the latter is oscillated and the,tool is rotated. While I have shown the recess equal in diameter to themirror, so that the edges of the latter engage the side Walls of therecess at all times, it is not necessary that this t be a close one. Thediameter of a recess can be somewhat larger than that of the Workwithout affecting the operation of the arrangement, since there is nodisadvantage encountered-ii the mirror slides and rotates relative tothe chuck and the hydrostatic cushion during the abrading operation solong as the mirror is given suilicient oscillation relative to the toolto prevent undesirable repetitive spot abrasion.

From the above description it is believed that it will be obvious thatthe present invention provides a work blocking arrangement which is inadvance over conventional arrangements in several respects. In additionto eliminating the need for skilled operators in blocking the work forthe abrading operation, it saves all of the time heretofore required inwaiting for the blocking pitch or wax to setand cool. It insures theapplication of a uniform pressure on all parts of the piece of Workduring the abrading operation and thus eliminates the possibility of thepiece being distorted due to the non-uniformity of applied pressurearising because of improper blocking and/or movement of the Work intooverhanging relation with the tool during the abrading operation. Whilethe arrangement is particularly desirable in the blocking of largepieces of work, since it permits the use of a much lighter blockingchuck, it will be readiliT appreciated that it Yis iuseful in blockingany type of work regardless of size and shape.

Although I have shown and described certain specific embodiments of myinvention, I am aware that many modifications thereof are possible. Myinvention therefore is not to be restricted to the speciiic details ofconstruction shown and described but is intended to cover allmodifications coming within the scope of th'e appended claims.

Havingk thus described my invention what I claim as ,-new anddesire tosecure by Letters Patent of the United states is: l

1. An apparatus for blocking a piece of work for abrading a surfacethereof comprising a chuck provided with a recess in which the piece ofWork is adapted to be seated with the surface to be abraded exposed andextending beyond the face of the chuck and with the edges of the workpartially confined by the side walls thereof, and a hydrostatic cushionbetween the bottom of said recess and the piece of work seated therein.

2. A blocking apparatus according to claim 1 in which said hydrostaticcushion comprises a .5 closed container made from an elastic materialand lled with a fluid.

3. A blocking apparatus according to claim 1 in which said hydrostaticcushion comprises a closed chamber made from an elastic material andfilled with a liquid.

4. A blocking apparatus according to claim 1 in which said hydrostaticcushion comprises a closed chamber made from an elastic material andfilled with a gas.

5. A blocking apparatus according to claim 1 in which said hydrostaticcushion comprises a spiral rubber tube having closed ends and filledwith a uid.

6. In an apparatus for abrading the front surface of a preformed opticalelement, th'e combination of a chuck provided with a recess in which theelement is adapted to be loosely conned as to both longitudinal andlateral movement and with front surface exposed, the bottom of saidrecess substantially complementary in shape to that of the rear surfaceof said element, a hydrostatic cushion loosely seated in the bottom ofsaid recess beneath and engaging the rear surface of said element, saidcushion being of such thickness as to space the element from the bottomof said recess and at the same time allow the element to seat thereinsufficiently so that the edges of the element are confined by the sidewalls of said recess; said cushion and element held in place in saidrecess by an abrading tool held against the front surface of saidelement by pressure between the chuck and tool.

7. An abrading apparatus according to claim 6 in which said hydrostaticcushion is fastened to the bottom of said recess, whereby only th'eoptical element is held in place in said recess by the tool.

JOHN R. TURNER.

